spi_txx9 controller driver

This is a driver for SPI controller built into TXx9 MIPS SoCs.
This driver is derived from arch/mips/tx4938/toshiba_rbtx4938/spi_txx9.c.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>